Chronic kidney disease (CKD) and cardiovascular disease (CVD), conditions with overlapping pathophysiologies, have emerged as major comorbidities among HIV-infected persons in the era of combination antiretroviral therapy. Some observational data implicate hepatitis C virus (HCV) as an independent risk factor for these conditions (in both HIV-uninfected and -coinfected populations). However, other studies failed to find associations between HCV and CKD or CVD. Moreover, it is challenging to completely account for important socioeconomic and behavioral confounders in observational studies. In the previous funding cycle of R01 DA026770, we established a cohort of approximately 300 participants - including dual uninfected, HIV monoinfected, HCV monoinfected, and HIV/HCV dual infected participants - with repeated measures of kidney injury markers, glomerular filtration rate by iohexol clearance from plasma (iGFR), vascular stiffness, and carotid intima-media thickness (IMT). We identified associations between HCV infection and iGFR slope, vascular stiffness, and carotid IMT. During the follow-up period of this cohort, which immediately preceded the availability of highly potent direct acting agents (DAAs), none of the HCV-infected participants received treatment for HCV. In this competing renewal, we propose a novel focus on the role of HCV in CKD and CVD, by leveraging previously collected data with targeted enrollment of HCV-infected (mono and dual) participants initiating treatment with newly available DAAs. In the next funding period, we propose to enroll an HCV treatment cohort - subjects preparing to initiate DAA-based HCV therapy - which will include both new recruits and participants followed previously (who begin DAAs in the current period). HCV treatment cohort subjects will have a minimum of one visit prior to starting DAA therapy and will then be followed for 36 months, the same as participants in the prior funding cycle. This approach will allow us to both assess pre- to post-HCV treatment biomarker changes in individual subjects (thereby eliminating inter-subject variability) and compare disease marker trajectories in the HCV treatment cohort with those in HCV-infected (but untreated) subjects followed in the prior period. Our aims are to 1) Determine the effect of HCV treatment with DAAs on kidney injury and function and on sensitive indicators of CVD in HCV mono and HIV/HCV dual- infected participants, and 2) Elucidate the effects of HCV treatment with DAAs on putative inflammatory and metabolic mediators of CKD and CVD. To accomplish these objectives, we have expanded our research team with expertise on HCV treatment and HCV immunology and immune activation. Determining whether HCV treatment with DAAs can abrogate kidney and cardiovascular pathogenesis can inform the evolution of HCV treatment guidelines.